Microvascular exchange and interstitial volume regulation in the rat: model validation

1988 ◽  
Vol 254 (2) ◽  
pp. H384-H399 ◽  
Author(s):  
J. L. Bert ◽  
B. D. Bowen ◽  
R. K. Reed
Keyword(s):  
Experimental Data ◽  
Osmotic Pressure ◽  
Plasma Proteins ◽  
Venous Pressure ◽  
Colloid Osmotic Pressure ◽  
Model Parameters ◽  
Transport Parameters ◽  
Interstitial Fluid Volume ◽  
Protein Tracers ◽  
Fitting Procedures

A dynamic mathematical model is formulated and used to describe the distribution and transport of fluid and plasma proteins between the circulation, interstitial space of skin and muscle, and the lymphatics in the rat. Two descriptions of transcapillary exchange are investigated: a homoporous "Starling model" and a heteroporous "plasma leak model." Parameters used in the two hypothetical transport mechanisms are determined based on statistical fitting procedures between simulation predictions and selected experimental data. These data consist of interstitial fluid volume and colloid osmotic pressure measurements as a function of venous pressure for muscle and interstitial colloid osmotic pressure vs. venous pressure for skin. The values determined for the transport parameters compare well with data in the literature. The fully determined model is used to simulate steady-state conditions of hypoproteinemia, overhydration, and dehydration, as well as the dynamic response to changes in venous pressure and intravascularly administered protein tracers. Comparisons between the simulation predictions and experimental data for these various perturbations are made. The plasma leak model appears to provide a better description of microvascular exchange.

Functional characteristics of the renal interstitium

1981 ◽  
Vol 241 (2) ◽  
pp. F105-F111 ◽  
Author(s):  
M. Wolgast ◽  
M. Larson ◽  
K. Nygren
Keyword(s):  
Hydrostatic Pressure ◽  
Osmotic Pressure ◽  
Plasma Proteins ◽  
Protein Transport ◽  
Fluid Transport ◽  
Colloid Osmotic Pressure ◽  
Capillary Membrane ◽  
Tubular Transport ◽  
Physical Forces ◽  
Capillary Fluid

The renal interstitial space analyzed as "inulin space" comprises about 13% in the rat. The Starling forces of this compartment are governed by the balance between tubular and capillary fluid transport and also by the leakage of plasma proteins from the blood side. Protein transport will occur in a large-pore system in the peritubular capillary membrane. During control antidiuresis, the interstitial hydrostatic pressure is 2-4 mmHg. The colloid osmotic pressure shows a larger variability but is generally about 5 mmHg. During conditions of depressed capillary reabsorption but unchanged tubular reabsorption, as in saline expansion, the interstitial hydrostatic pressure rises 3-4 times, whereas the colloid osmotic pressure will show a steep fall resulting from the increased fluid entry and unchanged protein transport. The interstitial volume increases only slightly, since it is compressed by the expanding tubules. The influence of interstitial physical forces on tubular transport remains unclear, mainly due to the inaccessibility of the lateral interspaces to direct measurement of relevant parameters.

Epithelial transport parameters: an analysis of experimental strategies

1983 ◽  
Vol 218 (1212) ◽  
pp. 309-329 ◽  
Keyword(s):  
Experimental Data ◽  
Epithelial Transport ◽  
Flux Ratio ◽  
Model Parameters ◽  
Acta Physiol ◽  
Transport Parameters ◽  
Na Transport ◽  
Experimental Conditions ◽  
System Parameters ◽  
Experimental Strategies

A set of experiments was simulated on a computer version of the Koefoed-Johnsen & Ussing model for high-resistance epithelia. The results obtained were analysed according to procedures commonly applied to the analyses of experimental data and interpreted in terms of the model parameters. Although the computer model encodes a stoichiometry of 3:2 for Na-K exchange through the Na pump, the simulation of published experimental procedures yields different figures in almost every case. We show that E Na as originally defined by Ussing & Zerahn ( Acta physiol. scand . 23, 110-127 (1951)) and as obtained from flux-ratio experiments has different values under different experimental conditions with unchanged system parameters and that it is distinct from E Na measured by other methods. We also show that unless the pump is saturated with internal Na an increase in the rate of pumping cannot cause a substantial increase in the rate of transepithelial Na transport.

Effects of plasma- and cell-free perfusates on filtration coefficient of perfused canine lungs

1985 ◽  
Vol 58 (5) ◽  
pp. 1521-1527 ◽  
Author(s):  
B. Rippe ◽  
M. I. Townsley ◽  
A. E. Taylor
Keyword(s):  
Osmotic Pressure ◽  
Whole Blood ◽  
Plasma Proteins ◽  
Protein Concentration ◽  
Complete Removal ◽  
Systemic Circulation ◽  
Colloid Osmotic Pressure ◽  
Filtration Coefficient ◽  
Plasma Protein Concentration ◽  
The Difference

The filtration coefficient (Kf,c) of the microvessels in isolated dog lungs were studied for whole and diluted blood, whole and diluted plasma, Tyrode's solution, and Tyrode's plus dextran (4%, 63,000 mol wt) perfusates. When whole blood and plasma were diluted, Kf,c increased abruptly at a plasma protein concentration between 4 and 5 g/l, an effect which was not dependent on the erythrocyte mass. Both Tyrode's and Tyrode's plus dextran produced increases in Kf,c (60 and 30%, respectively). The difference in Kf,c measured between these latter perfusates was completely abolished when Kf,c were corrected for viscosity differences. Thus the pulmonary microvasculature responds similarly to the systemic circulation in that complete removal of plasma proteins from the perfusate increases Kf,c by 50%. This effect is independent of erythrocyte mass or colloid osmotic pressure of the perfusate, since perfusion with dextran solutions alone also increased Kf,c.

Osmotic reflection coefficient for total plasma protein in lung microvessels

1985 ◽  
Vol 58 (2) ◽  
pp. 436-442 ◽  
Author(s):  
B. Rippe ◽  
M. Townsley ◽  
J. C. Parker ◽  
A. E. Taylor
Keyword(s):  
Weight Gain ◽  
Reflection Coefficient ◽  
Osmotic Pressure ◽  
Plasma Protein ◽  
Plasma Proteins ◽  
Colloid Osmotic Pressure ◽  
Initial Slope ◽  
Total Plasma ◽  
Gain Curve ◽  
Osmotic Reflection Coefficient

The osmotic reflection coefficient (sigma) for total plasma proteins was estimated in 11 isolated blood-perfused canine lungs. Sigma's were determined by first measuring the capillary filtration coefficient (Kf,C in ml X min-1 X 100g-1 X cmH2O-1) using increased hydrostatic pressures and time 0 extrapolation of the slope of the weight gain curve. Kf,C averaged 0.19 +/- 0.05 (mean +/- SD) for 14 separate determinations in the 11 lungs. Following a Kf,C determination, the isogravimetric capillary pressure (Pc,i) was determined and averaged 9.9 +/- 0.5 cmH2O for all controls reported in this study. Then the blood colloids in the perfusate were either diluted or concentrated. The lung either gained or lost weight, respectively, and an initial slope of the weight gain curve (delta W/delta t)0 was estimated. The change in plasma protein colloid osmotic pressure (delta IIP) was measured using a membrane osmometer. The measured delta IIP was related to the effective colloid osmotic pressure (delta IIM) by delta IIM = (delta W/delta t)0/Kf,C = sigma delta IIP. Using this relationship, sigma averaged 0.65 +/- 0.06, and the least-squares linear regression equation relating Pc,i and the measured IIP was Pc,i = -3.1 + 0.67 IIP. The mean estimate of sigma (0.65) for total plasma proteins is similar to that reported for dog lung using lymphatic protein flux analyses, although lower than estimates made in skeletal muscle using the present methods (approximately 0.95).

Sign in / Sign up

Export Citation Format

Share Document